The major principle here is trying to maintain and regulate moisture and keep anything that may already be rotting from affecting the rest of the bunch. Greens, obviously, have a lot of water in them. You want them to be able to retain that, without having much water on the surface of their leaves. Excessive moisture causes them to stick to the sides of the storage container or one another, thereby rotting more quickly. You also want to seal them in an airtight bag so they don’t get zapped of moisture once nestled in your fridge.